The present invention is generally related to the field of scanning technology and, more particularly, is related to a system and method for scanner calibration.
With the dawn of the information age, scanning technology that is employed to convert paper or other documents into digital documents plays an important role. In particular, scanning technology plays a very important role in reducing the amount of paper that is created in a typical business environment. Scanners contribute to an increase in the speed at which business affairs are conducted. For example, documents that are scanned into digital form may then be transmitted to recipients via the Internet or other network rather than using traditional mail or other couriers.
With all the promise and benefits of scanning technology, it still is plagued with various problems that may often prevent the faithful reproduction of hardcopy documents into digital form. For example, many scanners include inherent imperfections that mar the digital reproduction of scanned documents. Specifically, variations in optics such as lenses employed in scanners may contribute to less than perfect image creation. The various scanner sensors including those within sensor arrays may respond to power supply voltage differently and sensor output voltage ranges may vary from sensor to sensor. Also, variations in sensors generally exist due to process variations during the manufacturing. The light sources such as light emitting diodes (LEDs) employed in scanners often vary in their performance due to process variations as well.
In addition, typically scanners are plagued with sensor failure over time due to degradation, usage, and incidental damage, etc. For example, in some cases, over time a few sensors may experience failure and constantly emit a single output voltage due to damage or degradation. Such failure may manifest itself in the appearance of vertical streaks or lines in a digital document produced by such a scanner. Unfortunately, it is difficult to counter the effects of such errant sensors.
In view of the forgoing, the present invention provides for a system and method for calibrating an output from a sensor array in a scanner. In one embodiment, the system comprises a processor circuit having a processor and a memory. Stored on the memory and executable by the processor is the scanner calibration logic. The scanner calibration logic comprises logic for determining a minimum dark value for the sensor array, and logic for determining an optimum exposure time of a number of light sources associated with the sensor array. The scanner calibration logic also includes logic for determining a maximum white value for the sensor array at the exposure time, and logic for setting an analog offset based upon the minimum dark value. The scanner calibration logic further comprises logic for setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to a maximum white value.
The present invention may also be viewed as a method for calibrating an output from a sensor array in a scanner. In this regard, the present method comprises the steps of determining a minimum dark value for the sensor array; determining an optimum exposure time of a number of light sources associated with the sensor array; determining a maximum white value for the sensor array at the exposure time; setting an analog offset based upon the minimum dark value; and, setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to a maximum white value.
The system and method of the present invention help determine and disqualify malfunctioning sensors in the sensor array from operation. Consequently, the scanner may continue to be used without the negative effects of malfunctioning sensors such as streaks and other anomalies.